1. Field of the Invention
This invention relates to improvements in guard plates for rim cylinder locks.
2. Prior Art
For over fifty years workers in the art have been attempting to prevent cylinder locks from being defeated or violated by drilling, forcing, wrenching or pulling the cylinder. For early efforts in this regard see the patents to Phillips U.S. Pat. No. 1,979,139 (1926), Maxwell U.S. Pat. No. 1,579,126 (1926). Other workers in the art have continued to date with various arrangements of cylinder lock protectors none of which have been particularly successful commercially. Representative efforts are shown in the following U.S. Pat. Nos.: 3,083,563 (1963), 3,260,081 (1966), 3,550,411 (1970), 3,645,045 (1972), 3,768,284 (1973) 3,795,123 (1974), 4,041,741 (1977), 4,073,172 (1978), 4,139,999 (1979), 4,160,368 (1979), 4,237,712 (1980), 4,316,371 (1982). Even the most rugged cylinder guard can be defeated if the mounting means, e.g. bolts through the door, can be severed, or drilled out.
Commercially available guards include steel plates which are bolted over exposed faces of the cylinders leaving the cylinder plugs exposed through holes in the plates. These plates can be readily removed by chiseling or drilling the bolt heads or the bolt shanks. One prior art type of guard employs laminated plates with the bolt heads sandwiched between inner and outer plates and the outer plate hardened to prevent drilling. However, the laminated plates can be chiseled or peeled apart exposing the bolt heads, or the bolt shanks may be chiseled beneath the plates to remove the guard.
There is need in the art for a simple yet extremely rugged armored protective plate for shielding and protecting a rim cylinder lock from the outside which protects the lock cylinder itself and also has means to prevent the protective plate from being defeated by drilling or chiseling the mounting bolts.